1. Technical Field
The present invention relates to a power-splitting transmission wherein, regardless of how fast the internal combustion engine is spinning, a continuous variation from reverse gear to forward gear can be achieved by passing through a special position known as “engaged neutral”, in which the speed of movement of the vehicle is zero.
More precisely, its object is a power-splitting infinitely variable transmission having two modes of operation, wherein the constituent elements are distributed between two power trains that provide parallel connections between the internal combustion engine and the wheels of the vehicle, these means including at least two epicyclic gear sets, two electrical machines, one reducing gear stage and control means that guide the power between the input and output of the transmission differently depending on the mode of operation thereof.
2. Background Art
Power-splitting transmissions may be based on three known principles or modes of power splitting. According to the first mode, known as “coupled input”, the transmission is provided with a pair of power-splitting pinions that splits the power at the input of the mechanism and with an epicyclic “assembler” gear set that recombines the powers at the output of the mechanism. The control element is a variator.
In transmissions with power splitting of the “coupled output” type, there is provided, for example, a power-dividing planetary gear set at the input of the mechanism and a power-reassembling pair of pinions at the output of the mechanism, the control element again being a variator.
Finally, in transmissions with power splitting of the “two matching points” type, a first power-dividing epicyclic gear set can be positioned at the gearbox input, while a second power-reassembling epicyclic gear set is disposed at the gearbox output, the control element again being a variator.
The traditional infinitely variable transmissions (IVT) use only one or two of these three operating principles.
From U.S. Pat. Nos. 5,558,589 and 5,935,035 there are known infinitely variable transmissions with two modes of operation combining at least two planetary gear sets, two mode-changing clutches and one electrical variator, and using as the first mode of operation the principle of power splitting with coupled output.
According to these publications, the mode-changing means are positioned outside the epicyclic gear sets.
The significance in having two modes of operation available lies in the increase of the range of transmission ratios and in the possibility of reducing the size of the electrical machines.
Nevertheless, in these known two-mode architectures, the mode changes are achieved by multiple-disk clutches disposed on the transmission output, and for this reason are accompanied by torque jolts that are sensed as unpleasant by the users.
Another disadvantage of the architectures described in these publications lies in their complexity, which is related in particular to the presence of at least two clutches and one brake.